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comparison libcxx/include/__algorithm/shift.h @ 221:79ff65ed7e25

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LLVM12 Original
author Shinji KONO <kono@ie.u-ryukyu.ac.jp>
date Tue, 15 Jun 2021 19:15:29 +0900
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220:42394fc6a535 221:79ff65ed7e25
1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #ifndef _LIBCPP___ALGORITHM_SHIFT_H
10 #define _LIBCPP___ALGORITHM_SHIFT_H
11
12 #include <__config>
13 #include <__algorithm/move.h>
14 #include <__iterator/iterator_traits.h>
15
16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17 #pragma GCC system_header
18 #endif
19
20 _LIBCPP_PUSH_MACROS
21 #include <__undef_macros>
22
23 _LIBCPP_BEGIN_NAMESPACE_STD
24
25 // shift_left, shift_right
26
27 #if _LIBCPP_STD_VER > 17
28
29 template <class _ForwardIterator>
30 inline _LIBCPP_INLINE_VISIBILITY constexpr
31 _ForwardIterator
32 shift_left(_ForwardIterator __first, _ForwardIterator __last,
33 typename iterator_traits<_ForwardIterator>::difference_type __n)
34 {
35 if (__n == 0) {
36 return __last;
37 }
38
39 _ForwardIterator __m = __first;
40 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) {
41 if (__n >= __last - __first) {
42 return __first;
43 }
44 __m += __n;
45 } else {
46 for (; __n > 0; --__n) {
47 if (__m == __last) {
48 return __first;
49 }
50 ++__m;
51 }
52 }
53 return _VSTD::move(__m, __last, __first);
54 }
55
56 template <class _ForwardIterator>
57 inline _LIBCPP_INLINE_VISIBILITY constexpr
58 _ForwardIterator
59 shift_right(_ForwardIterator __first, _ForwardIterator __last,
60 typename iterator_traits<_ForwardIterator>::difference_type __n)
61 {
62 if (__n == 0) {
63 return __first;
64 }
65
66 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) {
67 decltype(__n) __d = __last - __first;
68 if (__n >= __d) {
69 return __last;
70 }
71 _ForwardIterator __m = __first + (__d - __n);
72 return _VSTD::move_backward(__first, __m, __last);
73 } else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) {
74 _ForwardIterator __m = __last;
75 for (; __n > 0; --__n) {
76 if (__m == __first) {
77 return __last;
78 }
79 --__m;
80 }
81 return _VSTD::move_backward(__first, __m, __last);
82 } else {
83 _ForwardIterator __ret = __first;
84 for (; __n > 0; --__n) {
85 if (__ret == __last) {
86 return __last;
87 }
88 ++__ret;
89 }
90
91 // We have an __n-element scratch space from __first to __ret.
92 // Slide an __n-element window [__trail, __lead) from left to right.
93 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
94 // over and over; but once __lead reaches __last we needn't bother
95 // to save the values of elements [__trail, __last).
96
97 auto __trail = __first;
98 auto __lead = __ret;
99 while (__trail != __ret) {
100 if (__lead == __last) {
101 _VSTD::move(__first, __trail, __ret);
102 return __ret;
103 }
104 ++__trail;
105 ++__lead;
106 }
107
108 _ForwardIterator __mid = __first;
109 while (true) {
110 if (__lead == __last) {
111 __trail = _VSTD::move(__mid, __ret, __trail);
112 _VSTD::move(__first, __mid, __trail);
113 return __ret;
114 }
115 swap(*__mid, *__trail);
116 ++__mid;
117 ++__trail;
118 ++__lead;
119 if (__mid == __ret) {
120 __mid = __first;
121 }
122 }
123 }
124 }
125
126 #endif // _LIBCPP_STD_VER > 17
127
128 _LIBCPP_END_NAMESPACE_STD
129
130 _LIBCPP_POP_MACROS
131
132 #endif // _LIBCPP___ALGORITHM_SHIFT_H